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Highly significant mean sum of squares due to genotypes revealed the existence of substantial amount of variation and significant differences among the genotypes for all the seed vigor parameters except seed density. Block effects were non-significant in all the cases. D² values corresponding to 276 possible comparison among 24 genotypes, taking two genotypes at a time, were computed separately. Based on these estimates of genetic divergence, the genotypes were grouped into six clusters (Table 1). The cluster I comprised of maximum number of thirteen genotypes followed by cluster II and III with three genotypes each. Cluster IV and V consisted two genotypes each whereas cluster VI had single genotype. The clusters contained genotypes of heterogeneous origin coming from different regions. Even the exotic lines were grouped with indigenous materials. This indicated lack of parallelism between genetic and geographic diversity.

Average intra- and inter-cluster distance (D values) among six clusters are given in Table 2. The intra-cluster distance varied from 0.11 to 7.79 and did not transgress the limits of any of the inter-cluster distances. The zero value of intra-cluster distance for cluster VI was due to only one genotype in the cluster, whereas cluster V showed highest intra-cluster distance (7.79) having two genotypes. Moreover, cluster I and II also have high intra-cluster distance (6.83), which include thirteen and three genotypes, respectively. It indicated that the genotypes of these clusters were genetically less divergent and almost parallel divergent.

Minimum divergence at inter-cluster level was recorded between clusters II and VI (8.92) followed by between clusters I and VI (9.05) indicating that genotypes of these clusters were genetically close.

Maximum average inter-cluster distance was observed between clusters II and III (19.32) and between clusters II and IV (15.91). The genotypes belonging to these clusters were found genetically most divergent. Hence, it would be logical to incorporate such genotypes in the breeding program. The intra-cluster group means of the characters reveal the main fraction of the clusters (Table 3). An examination of the varietal composition of the clusters indicated the cluster Ill and composed of relatively high vigorous genotypes because of high mean values of most of vigor parameters viz. standard germination, vigor indices, seed density, germination after accelerated aging, field emergence index and seedling establishment. The cluster II was consisted of low vigor genotypes. Thus, the genotypes of these two clusters hold great promise as parents to obtain promising hybrid combination and create further variability for seedling vigor parameters.

The main criterion for selection of genotypes and parents for hybridization using D² analysis is the inter- cluster distances. The genotypes included in clusters with maximum inter-cluster distances are, obviously, genetically more divergent. It can, therefore, be suggested that hybridization between most divergent high vigor parents included in cluster Ill (P5915, WH992, WH896) and poor vigorous genotypes (P5875, P5876, P5888) followed by selection in segregating generations may be useful in isolating the desirable strains promising for growing under sub-optimal environmental conditions.

Raut VM, Rao VSP, Patil VP and Deodikar Gb (1985) Genetic divergence in Triticum durum. Indian J Genet 45:141-151.

Sethi SK, Singh YP and Sheoran RK (1992) Genetic diversity in wheat. Crop Res (Suppl) 5: 129-135.